The present invention relates to a method for mounting, for instance, electronic parts onto circuit boards, and a part-mounting apparatus executing the method.
High accuracy and high productivity have been demanded in recent part-mounting apparatuses for mounting, age e.g., electronic parts onto circuit boards. For instance, a part-mounting apparatus of a multi-functional type has increased its market share, wherein a part transfer device (referred to as a head member hereinafter) taking out each electronic part from a part feed section and mounting it to a circuit board is moved by an XY robot which is freely movable in X, Y directions. In this type of the apparatus, parts can be supplied from the part feed section with a high degree of freedom in a feed state, a variety of parts can be handled and high accuracy of the mounting is secured because of a simple constitution, and accordingly furthermore development has been attempted with an aim for much higher speed and accuracy. In the meantime, besides the speed-up of mounting of parts by the adoption of a linear motor to the XY robot, a pressure of a part-sucking nozzle of the head member impressed to the parts has been controlled in a nozzle-driving mechanism of some apparatuses, thereby to adjust a mount pressure. Although a mechanism using a mechanically driving clutch has been a mainstream conventionally to take out the electronic parts from the part feed section and correct a posture of each held part simultaneously, the mechanism practically has demerits, that is, a complicated structure and an increased weight with impressing a high stress to the held part, etc. As such, in accordance with the progress of the image recognition technique, an air pressure is primarily utilized today to suck, take out, recognize and correct a position of the parts.
Parts to be mounted to circuit boards have become greatly complicate in shape consequent to the miniaturization of products with the circuit boards incorporated therein. As a result, some of the parts have no face to be able to be sucked by the nozzle. For coping with this, there is a part-mounting apparatus which includes a chucking mechanism with two holding plates moving in opposite directions to each other orthogonally to a thickness direction of the circuit board, wherein the posture of the part held by the holding plates is corrected through the image recognition technique.
A method for mounting parts which is carried out in the above-described part-mounting apparatus of the conventional art will be described with reference to the. drawings.
FIG. 8 is an example of a chucking device 200 set in the conventional part-mounting apparatus. The chucking device 200 generally consists of a chucking mechanism part 201 and a driving part 210 for moving the chucking mechanism part 201 in a thickness direction I of a circuit board. The chucking mechanism part 201 has two holding plates 202, 203 and an air pressure driving source 204 with, e.g., an air cylinder. The holding plates 202, 203 are movable in opposite directions II to each other orthogonally to the thickness direction I, and opened/closed by the driving source 204 to hold electronic parts. The driving part 210 and chucking mechanism part 201 are coupled via a spring 205 which absorbs shocks between the part and the chucking mechanism part 201 when the part is held by the chucking device 200 and between the part held by the chucking mechanism part 201 and the circuit board when the part is mounted to the circuit board.
The chucking device 200 in the above constitution is mounted to an XY robot as described earlier.
The method of mounting in the part-mounting apparatus having the above chucking device 200 will be specifically described below.
The chucking device 200 is moved by the XY robot to above a hold position of in the part feed section. The holding plates 202, 203 are opened by turning ON the air pressure driving source 204. At this time, the chucking device 200 recognizes an initial height IV of the part feed section from a placing face 421 and a height III of a held part 422 in the chucking mechanism part 201. The chucking mechanism part 201 is lowered by the driving part 210 a distance (IV-III) obtained by subtracting the height III from the initial height IV in a height direction of the part 422. A change in amount of the downward movement of the chucking mechanism part 201 as a result of a distortion of the placing face 421 or an error in the height III of the part 422 is absorbed by the spring 205. Thereafter, simultaneously with when the chucking mechanism part 201 is finished to move down or an operation delay time of the chucking mechanism part 201 earlier than the finish of the movement, the air pressure driving source 204 is turned OFF and the holding plates 202, 203 are closed thereby to hold the part 422. The driving part 210 raises the chucking mechanism part 201 concurrently when the part 422 is completely held. Taking out of the part 422 from the part feed section is completed in this manner. The chucking device 200 is then moved by the XY robot to a mount position on the circuit board, and the part 422 is mounted to the circuit board.
According to the conventional mount method as above, in the event that the initial height IV from the part placing face 421 in the chucking mechanism part 201 includes an error, for example, if the height IV in FIG. 9 is larger than a predetermined value, the chucking mechanism part 201 cannot hold the part 422 at a normal position, but holds the part 422 only at end portions of the holding plates 202, 203 at the side of the placing face 421, which gives rise to a gap V. In an extreme case, the chucking mechanism part 201 after holding the part 422 may drop the part 422 in the middle of transferring the part to the circuit board, or shift a posture of the part 422 when moving the part for the correction after the image recognition. In addition, the chucking mechanism part 201 is descended a total distance of an original fall distance and the gap V when mounting the part to the circuit board, and consequently impresses unnecessary impacts between the circuit board and part 422. On the other hand, if a fall position of the chucking mechanism part 201 to the part feed section is set to be closer to the part placing face 421 than an original position so as to avoid the unnecessary shocks when the part is mounted to the circuit board, the chucking mechanism part 201 in turn applies undesirable shocks to the part 422 when taking out the part 422.
The placing face 421 sometimes is considerably a fragile tray. As shown in FIG. 10, when the chucking mechanism part 201 applies a force to the part 422 unexpectedly from above when taking out the part 422, a part of the placing face 421 of a tray 423 is deformed, thereby bringing the part 422 into a greatly instable state. The part 422 in such instable state is highly possibly dropped or recognized wrong in any process of holding, image recognition, positional correction and mounting. Further, in such the fragile tray 423, the force acting to the part 422 may influence other parts on the same tray 423 to change an alignment of the other parts, forcing the other parts outside the tray 423 in the worst case.